Xray - Outcome 8 Flashcards
Cone-beam computed tomography (CBCT)
three-dimensional imaging is now available. In 1999 a technology termed cone-beam computed tomography (CBCT) was introduced that allows for the viewing of structures in the oral-maxillofacial complex in three dimensions. The adoption of three-dimensional digital imaging in dentistry has expanded since that time as the result of numerous technical improvements and commercial marketing. CBCT has become the desired technology because of the accurate and detailed information it provides.
Intra-Oral Radiographs
The conventional film placed inside the mouth is referred to as intra-oral. Intra-oral films are direct exposure films.
Extra-Oral Radiographs
Films exposed outside the mouth are referred to as extra-oral radiographs
This type of exposure is used when large areas of the jaw or skull need to be examined. Small periapical films cannot adequately cover the temporal-mandibular joint, the maxillary sinus, or broad areas of the jaw. However, extra-oral radiographs do not show details as well as periapical films. While extra-oral films are appropriate for evaluating large areas, they are not recommended for the detection of subtle changes such as carious lesions or periodontal defects.
Intra-Oral Radiograph
- Made intraorally.
- Use direct-exposure x-ray film.
- How individual teeth and surrounding bone.
- Tooth images, especially with the paralleling technique, are closer to actual size.
- Image outlined is usually more distinct and sharper.
- Usually requires prolonged patient cooperation for a full mouth series.
- It May require more time depending on the difficulty of the procedure and the cooperation of the patient.
- By determining horizontal angulation for individual teeth, the contacts can be opened.
Panograph
- Made extra orally.
- Use intensifying screens and screen-type x-ray film.
- Show the entire facial complex on one film.
- Due to increased distance between object and film, images are magnified.
- Image outline on entire radiograph slightly fuzzy; spinal shadow may cause some loss of detail.
- Usually requires less patient cooperation.
- Usually can be completed within 5 minutes (from initial positioning of the patient to completion of exposure).
- Usually produce overlapping of tooth contacts in the bicuspid and molar areas.
The 1st panoramic x-ray
The first machine of this type was the Panorex, and was introduced in 1959 by the S.S. White Company. Today, there are many types of panoramic x-ray machines made by different manufacturers; however, the basic principles of image formation are the same for most machines (Robinson, 2024).
Pantomography / Slit Bean Scanography
The most common panoramic technique used in dentistry is called pantomography. This method uses the principles of slit-beam scanography (collimation). A radiograph can be made by scanning an object with a thin, moving beam of X-rays. A slit-shaped collimator is used to make a narrow beam of X-rays. The X-ray tube is moved to scan different parts of the object. Before reaching the film, the X-ray beam passes through a hole in a sheet of heavy metal that acts as a scatter guard. The hole is shaped to the size of the primary beam and moves with the x-ray beam. The scatter guard prevents X-rays from reaching parts of the film not being exposed by the primary beam
A panoramic radiograph shows a sharp image of a layer of tissue with the layers above and below it being unsharp or blurred. The radiograph is made by moving the x-ray tube and film parallel to each other in opposite directions during film exposure. During the movement of the tube and film, the X-ray beam turns and is constantly directed at a point in the layer being examined. Thus, a tomogram shows both sharp and blurred X-ray shadows. The area where images are sharp is called the focal trough or image layer or zone of sharpness
The basic factors in rotational panoramic radiography include:
- A narrow vertical slit beam of X-rays is used to scan a stationary object
- The tubehead and film carrier are connected to each other; they circle around the object so that the X-ray beam turns around a pivotal point (rotation axis) in the object
- While the tube and film carrier are moving, the film also moves behind a scatter guard
- The film moves through the X-ray beam at the same rate as the layer being imaged in the object. Therefore, when one inch of film moves through the x-ray beam, the layer in the object where one inch of depth has been scanned by the beam appears sharp in the radiograph layers past that depth appear blurred
In order to produce a diagnostically acceptable panoramic radiograph, several steps must be followed precisely…
These include (1) preparation of the unit, (2) patient preparation, (3) patient positioning, (4) film exposure, and (5) film processing. If any of these steps are not performed correctly, the subsequent error may lead to an unacceptable radiograph
Steps for Panoramic Xray
- Operatory Preparation:
Turn on equipment.
Place required barriers.
Select a setting based on the patient’s stature and mode.
Ensure head calipers are open and all the way forward.
Select the correct setting for the patient based on the requisition and the stature of the patient:
P1-Adult
P10-child
BW1- bitewings
Select and insert the bite stick in the slot.
Prepare and place in the operatory appropriate PPE, Dixie cup, and disposable bite block.
- Patient Preparation:
Take time to explain the procedure to the patient and why this type of radiograph is required.
Remove any personal items from the patient’s head and neck area (all jewelry, appliances, glasses, hair pins, dentures).
Place a double-sided vest-type apron on the patient.
- Patient Positioning:
- Instruct the patient to stand in front of the machine, in front of the control mirror.
- Using the “up” or “down” arrow key, adjust the height of the unit so that the bite block and the anterior teeth and the anterior teeth are at the same height.
- Have the patient grab the handles.
- Have the patient bite into the indentation of the bite block.
- Swivel the mirror.
- Position the head of the patient in such a way that the occlusal plane is slightly inclined towards the anterior. (Chin is angled up slightly)
Switch on the light localizer with the key on the Control Panel. It is used for correct patient positioning. The Frankfort Horizontal Plane (FH) horizontal light beam should reflect between the upper edge of the external auditory canal and the lowest point of the infraorbital rim (tragus).
7. The height of the FH horizontal light beam can be adjusted with the slider
Fine-tune the head inclination for the FH setting
Align the center of the anterior teeth or of the face with the central light line
Press a key on the Control Panel to move the forehead support “towards forehead” until it touches the patient’s forehead and stops
Close the temple supports by pressing the key on the Control Panel until touching the patient’s “temples” and stop
8. Swivel mirror back
- Check the FH setting and the central light beam again to ensure the patient did not move
- Have the patient swallow and place his or her tongue against the palate
- Instruct the patient to breathe through their nose, close their eyes if they would like, and hold in position until the machine completes rotating.
- Expose the image and return the patient back to the operatory.
Three-dimensional imaging provides more detailed information & ability to…
ability to evaluate pathology (e.g., bony and soft tissue), distances to critical anatomic landmarks (e.g., maxillary sinus, mandibular canal), locations of impacted teeth, eruption patterns, or other concerns of the oral and maxillofacial complex.
Three-dimensional imaging provides the dental professional with a more complete interpretive image than traditional dental imaging…
- Three-dimensional imaging serves a number of diagnostic purposes for dental practitioners.
- Anatomic structures of the reconstructed volume of data provide accurate dimensional measurements of the patient with a 1:1 ratio relationship
- The essential components for three-dimensional imaging include a CBCT machine, a computer, and various types of viewing software.
- The advantages of three-dimensional imaging include a lower dose of radiation to the patient, a brief scanning time, anatomically accurate images, and the ability to easily save and transport the images.
- The disadvantages of three-dimensional imaging include patient movement artifacts, limited FOV size, cost of equipment, and lack of training in the interpretation of image data on areas outside of the maxilla and the mandible.
Equipment for CBCT (3-d)
The use of specialized equipment is necessary for three-dimensional digital imaging. The essential components for this type of imaging system include a CBCT machine, a computer, and viewing software.
CBCT Machine
The CBCT machine is comparable in size and appearance to a panoramic machine. With the CBCT machine, the patient sits, stands, or is placed in a supine position during the scanning process. In a single rotation, the source of radiation and the receptor capture the FOV. The radiation that exits the patient is received by a solid-state flat panel detector and becomes the raw data that is sent to the computer. Scan times vary between 7 and 30 seconds; shorter scan times are desirable to eliminate artifacts created by patient movement.
Computer - for CBCT
A computer connected to the CBCT machine accepts raw data and reconstructs the data into a stack of axial images (DICOM images). The computer has separate proprietary viewing software to import DICOM images. The reason for exposing the scan dictates the proper region of interest and therefore determines the FOV and correct spatial resolution.
